1. Field of the Invention
The present invention relates to variable magnification optical systems and, more particularly, to a variable magnification optical system having an image stabilizing function in which one lens unit, constituting a part of the variable magnification optical system, is so moved as to have directional components perpendicular to an optical axis to optically compensate for the shaking of a photographed image caused by the vibration (tilting) of the variable magnification optical system, thereby obtaining a stabilized image, and which optical system is suited to photographic cameras, electronic cameras, video cameras or the like.
2. Description of Related Art
When shooting is being performed by using a photographic system on a running car, or flying air plane, or the like moving vehicle, the vibrations propagate to the photographic system, thereby causing the shaking of a photographed image in some cases. Also, when not on the moving vehicle, but when the photographer unstably holds the photographic system by the hand, it often happens that the vibration of the hand causes the shaking of a photographed image. As the focal length of the photographic system increases to the telephoto region, in particular, the frequency of occurrence of the shaking of a photographed image increases rapidly.
Heretofore, there have been proposed a variety of optical systems having an image stabilizing function of preventing the shaking of a photographed image from occurring in such situations.
For example, in Japanese Laid-Open Patent Application No. Hei 5-232410, there is disclosed a zoom lens of the telephoto type comprising four lens units of positive, negative, positive and positive refractive powers in this order from the object side, wherein the second lens unit is made to move in directions perpendicular to an optical axis, thereby stabilizing the image.
In another Japanese Laid-Open Patent Application No. Hei 7-152002, there is disclosed a zoom lens comprising four lens units of negative, positive, negative and positive refractive powers in this order from the object side, wherein the third lens unit is made to move in directions perpendicular to an optical axis, thereby stabilizing the image.
Also, in Japanese Laid-Open Patent Application No. Hei 7-199124, there is disclosed a variable magnification optical system comprising four lens units of positive, negative, positive and positive refractive powers in this order from the object side, wherein the entirety of the third lens unit is made to move in directions perpendicular to an optical axis, thereby stabilizing the image.
In general, an image stabilizing optical system in which a lens constituting a part of the optical system is made to decenter in parallel with directions perpendicular to the optical axis so as to stabilize the image, has such an advantage that there is no need to use an additional special optical element for stabilizing the image.
However, this method requires creation of a space in which to move the moving lens unit. Another problem of this method is that, if an improper one of the lens units is selected to decenter in parallel, the produced amount of decentering aberrations becomes larger.
The present invention is applied to a variable magnification optical system in which a lens unit constituting a part of the variable magnification optical system is so moved as to have directional components perpendicular to an optical axis to compensate for the shaking of an image caused by the vibration (tilting) of the variable magnification optical system, and sets forth appropriate rules of design for the form and the construction and arrangement of the constituent lenses of the variable magnification optical system. It is, therefore, an object of the invention to provide a variable magnification optical system having an image stabilizing function with the bulk and size of the entire system reduced to a compact form, with the operating system simplified in structure and with the load on the driving means lowered, while, when the lens unit is made to decenter to compensate for the shaking of an image, still permitting the produced amount of decentering aberrations to be suppressed to a minimum.
To attain the above object, in accordance with an aspect of the invention, there is provided a variable magnification optical system having an image stabilizing function, which comprises, in order from an object side, a first lens unit of negative refractive power, a second lens unit of positive refractive power, a third lens unit of negative refractive power and a fourth lens unit of positive refractive power, wherein the separation between every successive two of the first to fourth lens units is varied to effect variation of magnification, and the third lens unit is so moved as to have directional components perpendicular to an optical axis to compensate for shaking of an image caused by vibration of the variable magnification optical system, the variable magnification optical system satisfying the following conditions:
D1W greater than D1Txe2x80x83xe2x80x83(1)
D2W less than D2Txe2x80x83xe2x80x83(2)
D3W greater than D3Txe2x80x83xe2x80x83(3)
1.5 less than |f3|/f2 less than 2.5xe2x80x83xe2x80x83(4)
2.1 less than f4/f2 less than 10xe2x80x83xe2x80x83(5)
where DiW and DiT are separations between the i-th lens unit and the (i+1)st lens unit in a wide-angle end and in a telephoto end, respectively, and fi is the focal length of the i-th lens unit.